Comments: In the reverse reaction, the 2'-hydroxyisoflavone (2'-hydroxydaidzein) is reduced to an isoflavanone. Also acts on 2'-hydroxyformononetin and to a small extent on 2'-hydroxygenistein. Involved in the biosynthesis of the phytoalexin glyceollin. The isoflavones biochanin A, daidzein and genestein as well as the flavonoids apigenin, kaempferol and quercetin do not act as substrates.

Comments: The enzyme, which participates in the aerobic (late cobalt insertion) pathway of adenosylcobalamin biosynthesis, catalyses the reduction of the double bond between C-18 and C-19 of precorrin-6A. See EC 1.3.1.106, cobalt-precorrin-6A reductase, for the corresponding enzyme that participates in the anaerobic cobalamin biosynthesis pathway.

Comments: Highly specific for 4-hydroxynon-2-enal and non-2-enal. Alk-2-enals of shorter chain have lower affinities. Exhibits high activities also for alk-2-enones such as but-3-en-2-one and pent-3-en-2-one. Inactive with cyclohex-2-en-1-one and 12-oxophytodienoic acid. Involved in the detoxication of α,β-unsaturated aldehydes and ketones [cf. EC 1.3.1.102, 2-alkenal reductase (NADP+)].

Comments: The enzyme, found in higher plants, green algae, and some phototrophic bacteria, is involved in the production of monovinyl versions of (bacterio)chlorophyll pigments from their divinyl precursors. It can also act on 3,8-divinyl chlorophyllide a. cf. EC 1.3.7.13, 3,8-divinyl protochlorophyllide a 8-vinyl-reductase (ferredoxin).

Comments: This enzyme catalyses the second of three steps leading to the formation of siroheme from uroporphyrinogen III. The first step involves the donation of two S-adenosyl-L-methionine-derived methyl groups to carbons 2 and 7 of uroporphyrinogen III to form precorrin-2 (EC 2.1.1.107, uroporphyrin-III C-methyltransferase) and the third step involves the chelation of ferrous iron to sirohydrochlorin to form siroheme (EC 4.99.1.4, sirohydrochlorin ferrochelatase). In Saccharomyces cerevisiae, the last two steps are carried out by a single bifunctional enzyme, Met8p. In some bacteria, steps 1-3 are catalysed by a single multifunctional protein called CysG, whereas in Bacillus megaterium, three separate enzymes carry out each of the steps, with SirC being responsible for the above reaction.

Comments: The enzyme participates in the flavonoid biosynthesis pathway found in plants. It catalyses the double reduction of anthocyanidins, producing (2R,3R)-flavan-3-ol monomers required for the formation of proanthocyanidins. While the enzyme from the legume Medicago truncatula (MtANR) can use both NADPH and NADH as reductant, that from the crucifer Arabidopsis thaliana (AtANR) uses only NADPH. Also, while the substrate preference of MtANR is cyanidin>pelargonidin>delphinidin, the reverse preference is found with AtANR. cf. EC 1.3.1.112, anthocyanidin reductase [(2S)-flavan-3-ol-forming].

Comments: Arogenate dehydrogenases may utilize NAD+ (EC 1.3.1.43), NADP+ (EC 1.3.1.78), or both EC 1.3.1.79). NADP+-dependent enzymes usually predominate in higher plants.The enzyme from the cyanobacterium Synechocystis sp. PCC 6803 and the TyrAAT1 isoform of the plant Arabidopsis thaliana cannot use prephenate as a substrate, while the Arabidopsis isoform TyrAAT2 can use it very poorly [2,3].

Comments: Arogenate dehydrogenases may utilize NAD+ (EC 1.3.1.43), NADP+ (EC 1.3.1.78), or both (EC 1.3.1.79). Enzymes that can utilize both cofactors have been reported from some Proteobacteria, including Burkholderia caryophylli, Burkholderia cepacia, Pseudomonas marginata and Delftia acidovorans.

Comments: NADH cannot replace NADPH as reductant. The Δ8,9-double bond of (+)-cis-isopulegone and the Δ1,2-double bond of (±)-piperitone are not substrates. The enzyme from peppermint (Mentha x piperita) converts (+)-pulegone into both ()-menthone and (+)-isomenthone at a ratio of 70:30 for native enzyme but it does not catalyse the reverse reaction. This enzyme is a member of the medium-chain dehydrogenase/reductase superfamily.

Comments: The reaction occurs in the opposite direction to that shown above. The enzyme participates in the menthol-biosynthesis pathway of Mentha plants. (+)-Pulegone, (+)-cis-isopulegone and ()-menthone are not substrates. The enzyme has a preference for NADPH as the reductant, with NADH being a poor substitute [2]. The enzyme is highly regioselective for the reduction of the endocyclic 1,2-double bond, and is stereoselective, producing only the 1R-configured product. It is a member of the short-chain dehydrogenase/reductase superfamily.

Comments: Catalyses a step in the 3-hydroxypropanoate/4-hydroxybutanoate cycle, an autotrophic CO2 fixation pathway found in some thermoacidophilic archaea [1]. The enzyme from Sulfolobus tokodaii does not act on either NADH or crotonyl-CoA [2]. Different from EC 1.3.1.8, which acts only on enoyl-CoA derivatives of carbon chain length 4 to 16. Contains Zn2+.

Comments: The reaction is catalysed in the reverse direction. This enzyme, isolated from the bacterium Rhodobacter sphaeroides, catalyses (E)-but-2-enoyl-CoA-dependent oxidation of NADPH in the presence of CO2. When CO2 is absent, the enzyme catalyses the reduction of (E)-but-2-enoyl-CoA to butanoyl-CoA, but with only 10% of maximal activity (relative to (E)-but-2-enoyl-CoA carboxylation).

Comments: Catalyses the reaction in the reverse direction. This enzyme from Streptomyces collinus is specific for (E)-but-2-enoyl-CoA, and is proposed to provide butanoyl-CoA as a starter unit for straight-chain fatty acid biosynthesis.

Comments: Cloned from Artemisia annua. In addition to the reduction of artemisinic aldehyde it is also able to a lesser extent to reduce artemisinic alcohol and artemisinic acid. Part of the biosyntheis of artemisinin.

Comments: The reaction occurs in the reverse direction with reduction of the terminal double bond next to the alcohol group. Isolated from human fetal brain tissue but present in all eukaryotes. In mammalian cells dolichols are predominantly 18-21 isoprene units in length.

Comments: Contains FAD. The reaction is catalysed in the opposite direction to that shown. The enzyme from the bacterium Clostridium propionicum is a complex that includes an electron-transfer flavoprotein (ETF). The ETF is reduced by NADH and transfers the electrons to the active site. Catalyses a step in a pathway for L-alanine fermentation to propanoate [1]. cf. EC 1.3.1.84, acrylyl-CoA reductase (NADPH).

Comments: Isolated from the green alga Botryococcus braunii BOT22. Acts in the reverse direction. Involved in the production of botryococcenes, which are triterpenoid hydrocarbons of isoprenoid origin produced in large amount by this alga.

Comments: Contains FMN. The enzyme participates in the biosynthesis of fumigaclavine C, an ergot alkaloid produced by some fungi of the Trichocomaceae family. The enzyme catalyses the reduction of chanoclavine-I aldehyde to dihydrochanoclavine-I aldehyde. This hydrolyses spontaneously to form 6,8-dimethyl-6,7-didehydroergoline, which is converted to festuclavine by EC 1.5.1.44, festuclavine dehydrogenase.

Comments: A flavoprotein (FAD). The enzyme from the archaeon Thermoplasma acidophilum is involved in the biosynthesis of membrane lipids. In vivo the reaction occurs in the reverse direction with the formation of 2,3-bis-O-phytanyl-sn-glycerol 1-phosphate. cf. EC 1.3.99.34, 2,3-bis-O-geranylgeranyl-sn-glycerol 1-phosphate reductase (donor).

Comments: Shows highest activity with 1-nitrocyclohexene but also has significant activity with 2-methylpentenal and trans-cinnamaldehyde [3]. Involved in the detoxication of α,β-unsaturated aldehydes and ketones. Has very low activity with NAD as reductant (cf. EC 1.3.1.74, 2-alkenal reductase [NAD(P)+]).

Comments: The enzyme completes each cycle of fatty acid elongation by catalysing the stereospecific reduction of the double bond at position 2 of a growing fatty acid chain, while linked to the acyl-carrier protein, in an NADPH-dependent manner. This entry stands for enzymes whose stereo-specificity with respect to NADP+ is not known. [cf. EC 1.3.1.39 enoyl-[acyl-carrier-protein] reductase (NADPH, Re-specific), EC 1.3.1.10, enoyl-[acyl-carrier-protein] reductase (NADPH, Si-specific) and EC 1.3.1.9, enoyl-[acyl-carrier-protein] reductase (NADH)].

Comments: In the fruit-ripening process of strawberry (Fragaria x ananassa) the reaction is catalysed in the reverse direction from that shown. 4-hydroxy-2,5-dimethylfuran-3(2H)-one is one of the major aroma compounds in the fruits. The enzyme has also been detected in tomato (Solanum lycopersicum) fruits [2]. NADPH is the preferred cofactor.

Comments: The enzyme, which participates in the anaerobic (early cobalt insertion) pathway of adenosylcobalamin biosynthesis, catalyses the reduction of the double bond between C-18 and C-19 of cobalt-precorrin-6A. The enzyme from the bacterium Bacillus megaterium has no activity with NADPH. See EC 1.3.1.54, precorrin-6A reductase, for the corresponding enzyme that participates in the aerobic cobalamin biosynthesis pathway.

Comments: The enzyme, purified from the California poppy (Eschscholzia californica), is involved in detoxifying the phytoalexin sanguinarine produced by poppy itself (cf. EC 1.5.3.12, dihydrobenzophenanthridine oxidase), when it binds to the cell wall of the poppy cell. The reaction with NADPH is up to three times faster than that with NADH at low concentrations (<10 μM) of the dinucleotide. At higher concentrations the reaction with NADPH is inhibited but not that with NADH [1].

Comments: The enzyme, characterized from the bacterium Acetobacterium woodii, contains two [4Fe-4S] clusters and FAD. The enzyme couples the endergonic ferredoxin reduction with NADH as reductant to the exergonic reduction of caffeoyl-CoA with the same reductant. It uses the mechanism of electron bifurcation to overcome the steep energy barrier in ferredoxin reduction. It also reduces 4-coumaroyl-CoA and feruloyl-CoA.

Comments: This flavin containg enzyme, isolated from the bacteria Acidaminococcus fermentans and butanoate-producing Clostridia species, couples the exergonic reduction of (E)-but-2-enoyl-CoA to butanoyl-CoA with NADH to the endergonic reduction of ferredoxin by NADH, using electron bifurcation to overcome the steep energy barrier in ferredoxin reduction.

Comments: The enzyme catalyses the successive reduction of the geranylgeraniol esterifying group to phytol, reducing three out of four double bonds, and transforming geranylgeranyl bacteriochlorophyllide a via dihydrogeranylgeranyl bacteriochlorophyllide a and tetrahydrogeranylgeranyl bacteriochlorophyllide a to bacteriochlorophyll a. The enzyme can also accept the pheophytin derivative geranylgeranyl bacteriopheophytin, converting it to bacteriopheophytin a.

Comments: The enzyme, characterized from Vitis vinifera (grape), participates in the flavonoid biosynthesis pathway. It catalyses the double reduction of anthocyanidins, producing a mixture of (2S,3S)- and (2S,3R)-flavan-3-ols. The enzyme catalyses sequential hydride transfers to C-2 and C-4, respectively. Epimerization at C-3 is achieved by tautomerization that occurs between the two hydride transfers. cf. EC 1.3.1.77, anthocyanidin reductase [(2R,3R)-flavan-3-ol-forming].

Comments: The enzyme, characterized from the bacteria Streptomyces griseus and Streptomyces coelicolor, is involved in the biosynthesis of γ-butyrolactone autoregulators that control secondary metabolism and morphological development in Streptomyces bacteria.

Comments: Contains flavin. The enzyme, characterized from the bacterium Clostridium scindens, participates in the bile acid 7α-dehydroxylation pathway. The enzyme catalyses two subsequent reductions of the double bonds within the bile acid A/B rings, following 7α-dehydration.

Comments: Contains flavin. The enzyme, characterized from the bacterium Clostridium scindens, participates in the bile acid 7α-dehydroxylation pathway. The enzyme catalyses the stereo-specific oxidation of its substrates and has no activity with the 7β anomers. cf. EC 1.3.1.116, 7β-hydroxy-3-oxochol-24-oyl-CoA 4-desaturase.

Comments: Contains FAD and FMN. The enzyme, characterized from the bacterium Clostridium scindens, participates in the bile acid 7α-dehydroxylation pathway. The enzyme catalyses the stereo-specific oxidation of its substrate and has no activity with the 7α anomer. cf. EC 1.3.1.115, 3-oxocholoyl-CoA 4-desaturase.

Glossary: meromycolic acids are one of the two precursors of the mycolic acids produced by Mycobacteria. They consist of a long chain typically of 50-60 carbons, which is functionalized by different groups.

Comments: InhA is a component of the fatty acid synthase (FAS) II system of Mycobacterium tuberculosis, catalysing an enoyl-[acyl-carrier-protein] reductase step. The enzyme acts on very long and unsaturated fatty acids that form the meromycolic component of mycolic acids. It extends FASI-derived C20 fatty acids to form C60 to C90 mycolic acids. The enzyme, which forms a homotetramer, is the target of the preferred antitubercular drug isoniazid.

Comments: This bacterial enzyme can transform various dihydrodiols of chlorobenzenes into the respective catechols, including the dihydrodiols of mono-, di-, tri-, and tetra-chlorinated benzenes. It also accepts the dihydrodiols of various chlorotoluenes. Substrates for the enzyme are generated by the broad spectrum EC 1.14.12.26, chlorobenzene dioxygenase.

Comments: The enzyme, characterized from the bacterium Streptomyces collinus, is involved in a pathway that transforms shikimate to cyclohexane-1-carbonyl-CoA by a series of dehydration and double-bond reduction steps. Most of the steps in this process occur with the carboxylic acid activated as a coenzyme A thioester. The enzyme catalyses three steps in this pathway, also acting on (3R,4R)-3,4-dihydroxycyclohexa-1,5-diene-1-carbonyl-CoA and (5S)-5-hydroxycyclohex-1-ene-1-carbonyl-CoA.

Comments: Isolated from the plants Catharanthus roseus, Olea europaea (common olive), and several Nepeta species. The enzyme reduces 8-oxogeranial, generating an unstable product that is subsequently cyclized into several possible products, either non-enzymically or by dedicated cyclases. The products, known as iridoids, are involved in the biosynthesis of many indole alkaloids. cf. EC 1.3.1.123, 7-epi-iridoid synthase.

Comments: The enzyme, characterized from the plant Antirrhinum majus (snapdragon), is involved in biosynthesis of 7-epi-iridoids such as antirrhinoside. The enzyme catalyses the stereospecific reduction of 8-oxogeranial, forming an unstable product that in the absence of additional cylases undergoes spontaneous cyclization to ()-cis,trans-nepetalactol. cf. EC 1.3.1.122, (S)-8-oxocitronellyl enol synthase.